The Canadian organist, pianist, teacher, composer, and lecturer, George MacKenzie Brewer, studied in Montreal with Percival J. Illsley in his childhood. Nevertheless, he was largely self-taught and was an avid reader on all subjects.

George MacKenzie Brewer was organist at Bethlehem Congregational Church in 1908, and by 1912 he had moved to the Church of the Messiah where he stayed until his death. He also served as organist at Temple Emanu-El, Westmount (Montreal), and as accompanist for the Montreal Elgar Choir (1923-1931). He was the pianist with the Dubois String Quartet in many concerts (1922-1929), he accompanied the violinist Saul Brant, and he later gave organ recitals for the Casavant Society.

Brewer was an examiner at the Dominion College Of Music (1907-1947) and taught at the Conservatoire de musique du Québec (CMM) (1944-1947), under whose auspices he gave series of recitals demonstrating the history of organ music. He also taught piano, organ, and theory privately. Brewer travelled widely (1913-1935), his interest in the native musics of various countries taking him as far as Eastern Europe and North Africa. His experiences made him an able lecturer on exotic and contemporary music and on visual art and philosophy, as well as on dramatic music, organ history, and Bach. He was a reviewer for the Montreal Daily Star and wrote program notes for the Canadian Society of Microbiologists (CSM) (1943-1947). From 1910 he was Fellow of the American Guild of Organists.

His compositions (itemized in Catalogue of Canadian Composers) include choral works, short piano pieces, and many songs, some published by Édition Belgo-Canadienne, Boston Music, and in La Lyre. One of his piano compositions, Trois Préludes, has been reprinted in CMH, Vol. 6. He also composed incidental music for Montreal Repertory Theatre productions, in some of which he appeared as an actor. With his broad culture and many skills he contributed significantly to Montreal's cultural development in the first half of the 20th century. A memorial concert was held in his honour on May 25, 1948 at the Church of the Messiah under CMM auspices. The National Library Of Canada holds many of his papers.